Indicates the key that is registered with the MGC. The key cannot be modified, read, or written by the operator without authority, so the hwH248MedGwyRegisterKey and hwH248MedGwyOperKey must be also provided to query and modify the hwH248MedGwyRegisterKey. The conditions for querying and modifying the hwH248MedGwyRegisterKey are as follows: 1) The hwH248MedGwyRegisterKey can return the correct query result only when the hwH248MedGwyOperKey is correct. Otherwise, the query fails; 2) The hwH248MedGwyRegisterKey can be set successfully only when the hwH248MedGwyOperKey is correct. Otherwise, the setting fails. This parameters must be 8..32 characters long to set. 0 indicate invalid string.